Gas and Oil Home Heating Furnaces - Bryant - Bad Control Module or Thermostat?

Hello,

I have a 1990 Bryant gas furnace that is acting up...
When the programmable thermostat is in the AUTO setting the blower wants to stop, start, stop, start about a second apart. The fan works fine if I put the the thermostat in th FAN ON mode but right when I move it to AUTO the blower trys to turn on, and off, on, off...

The air filter is clean, and the only reason I mention a possible Control module is because it was replaced about 5 years ago when the fan was always on.

Thanks in advance for any help!

bob

Assuming it's doing this in cooling mode from the description it sounds like a t-stat problem. If it's doing this in heating mode it could be either t-stat or board. In most set ups in cooling mode the t-stat just make an internal switch to the same contact as "fan on". So what mode is it acting up in? Heating or cooling?

In response to whether the thermostat is in heating or cooling mode: Neither/both...
Great question! Now I have to think it is the thermostat since the thermostat has a setting that says if the temperature is out of the range then either fire up the heat or the Air. So, I set the thermostat for the range of 65 and 82 so if the temp is below 65 the heat turns on and above 82 the air turns on. The temp in the house was/is within the range 73 so nothing should be happening. But still the blower wants to start/stop/start/stop.

Sounds like the thermostat??? I will pick up a cheap one to try.

Opinion?

Thanks,
bob

remove the Green wire (or wire that goes to G terminal)

if it fixes the problem, tstat is at fault

i am VERY familiar with the reason you replaced the board, i have replaced many myself

Well how about this....
It started working normally last night, which means something will go wrong on the coldest day of the year right?

I had left the circuit breaker, saftey switch, and thermostat off until I could work on it last night but when I turned everything on it was working fine. No on/off/on/off or fan constantly blowing (in the AUTO mode).

Is there anything I should test to make sure something is not going to break in the near future?

If I do remove the green wire what should happen, the fan stop blowing or the on/off should stop (when this happens a gain).

Thanks in advance!

removing the green wire will keep the tstat from energizing the fan relay. if it still cycles as you describe, rule out the tstat

is it a HUNTER tstat?